UPDATE: It’s official. Scott Lauber of the Boston Herald reports that Matsuzaka has been placed on the disabled list. Alfredo Aceves will take his place in the starting rotation Saturday against the Cubs.

6:50 PM:Daisuke Matsuzaka was sent for an MRI on his elbow Tuesday, the Boston Globe reports, and is expected to go on the disabled list after giving up five runs and walking seven in 4 1/3 innings in an ugly outing against the Orioles on Monday night.

Matsuzaka had two brilliant starts for the Red Sox last month, allowing two hits over 15 scoreless innings against the Blue Jays and Angels, before leaving his April 29 outing with elbow tightness. The Red Sox said that was strictly a precaution, but he hasn’t pitched well in his three outing since, including his relief loss in extra innings against the Angels on May 4.

“It has not been ready yet. We don’t really have much to discuss,” Terry Francona said of the MRI. “We’re talking about his elbow. Whether it’s sore or whether he’s afraid to get to a point where it will get sore, we’re trying to figure it out.”

The Boston Herald’s Scott Lauber pointed out that it may be something else entirely, tweeting the following:

For what it’s worth, pitching coach Curt Young believes Daisuke Matsuzaka’s issues last night were a product of illness, not injury

But whether he’s truly hurt or not, it looks like Dice-K will join John Lackey on the DL for Boston. Reliever Michael Bowden is expected to be added to the roster in his place.